BIOLOGY 12 – RESPIRATORY SYSTEM
• RESPIRATION: not just breathing
• breathing is just one part of this process
• can be divided into 4 areas:
Breathing
External
Respiration
Internal
Respiration
Cellular
Respiration
the movement of air into and out of the lungs
the exchange of O2 and CO2 between the
lungs and the BLOOD
the exchange of O2 and CO2 between BLOOD
and TISSUE FLUID
the process which produces ATP in
mitochondria --> requires O2 and releases CO2
BREATHING: BRINGING AIR TO THE LUNGS
• "INSPIRATION" - breathing air in
• "EXPIRATION" - breathing air
out
1. Air enters the nasal passages.
• Hairs and CILIA trap dust and
debris
• The air is warmed and
moistened.
• When we breathe, the GLOTTIS (the opening to the
LARYNX ("voice box")) is open, and when we swallow,
the EPIGLOTTIS covers the glottis.
3. Air enters the larynx. It is like a triangular box with the
Adam's Apple at the front corner.
• Elastic ligaments called VOCAL CORDS stretch from the
back to the front of the larynx just at the sides of the
glottis.
Vocal Chord
• These cords vibrate
when air is expelled past
them through the glottis.
Glottis
This vibrations produce
Wide Glottis
Narrow Glottis
sound.
Low Pitch
High Pitch
1.
2.
3.
4.
5.
6.
7.
8.
10.
2. The warmed and moistened air
passes through the PHARYNX (a common passage for
food and air).
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5. The trachea divides into two BRONCHI, which branch
into many smaller passages called bronchioles that
extend into the lungs.
6. The bronchioles continue to branch
out, and as they do, their walls get
thinner and diameter smaller.
Each bronchiole ends in sacs
called ALVEOLI, which fill up much
of the lungs.
• There are approximately 300
million alveoli per lung, for a total
of 150 m2 of alveolar area (at least
Capillary network around alveoli
40 time the area of the skin).
• Each alveolar sac is enclosed by a single layer of simple
epithelial tissue, which is surrounded by CAPILLARIES
carrying deoxygenated blood. GAS EXCHANGE occurs
between blood and air in alveoli.
• Lungs are enclosed by two pleural membranes. One
pleural membrane lines the chest walls, and an inner
membrane lines the lung. In between is fluid. This makes
for an air-tight seal.
INSPIRATION
• special ciliated cells at the top recesses of the nasal
cavities are scent receptors
EXPIRATION
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4. The air enters the TRACHEA (windpipe). The trachea is
held open by cartilaginous rings, and is lined with ciliated
mucous membranes.
• The cilia beat upward to move up mucus and any dust or
particles that were inhaled or accidentally swallowed.
Smoking can destroy cilia.
• Tracheotomy: an operation in which an incision is made
into the trachea below a blockage (and a tube is then
inserted).
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Mechanics of Breathing
• What powers
breathing? Creating
“negative pressure”
powers breathing.
Negative pressure is
EXPIRATION
INSPIRATION
air pressure that is
less (756 mm Hg) than the pressure of the surrounding
air (760 mm Hg). This negative pressure is created by
increasing the volume inside the thoracic cavity. Air
will naturally move in to fill this partial vacuum. The space
in the thoracic cavity is made bigger by the
CONTRACTION of the diaphragm muscle (this makes it
move downward and become less dome shaped). When
the diaphragm contracts, the space within lungs
increases.
• The muscles attached to the ribs, called intercostal
muscles, will also CONTRACT when you breathe in.
This contraction pulls the ribs up and out, further
increasing the space within the thoracic cavity.
• The air pressure in the lungs becomes less than the
atmospheric pressure. Air naturally rushes into the lungs
to fill this natural vacuum.
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CONTROL OF BREATHING
• When the DIAPHRAGM RELAXES, it moves up, and
when the INTERCOSTAL MUSCLES RELAX, the ribs
move down and inward. This decreases the volume in
the thoracic cavity, and air is forced out of the lungs
(expiration).
• CO2 & H+ IN THE BLOOD control the BREATHING
RATE
1. CO2 levels in blood increase as cells continue to produce
it
- The concentration of CO2 will increase until they
reach a threshold level
2. Chemoreceptors in arteries detect the increased CO2 &
H+ levels
3. chemoreceptors send a signal to a breathing center in
the MEDULLA OBLONGATA of the brain(it detects the
rising levels of CO2 and H+, but not affected by low O2
levels)
- also chemoreceptors in the carotid bodies(in carotid
arteries), and in the aortic bodies(in aorta) that
respond primarily to H+ concentration, but also to the
level of carbon dioxide and oxygen in the blood(these
bodies communicate with respiratory center)
4. medulla oblongata sends a nerve impulse to the
diaphragm & muscles in the rib cage
5. diaphragm contracts & lowers, while the rib cage moves
up
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6. air flows into alveoli, & alveolar walls expand & stretch
7. Stretch Receptors in the alveoli walls detect this
stretching
8. nerves in alveoli send signal to brain to inhibit the
medulla oblongata from sending its message to the
diaphragm and rib muscles to contract (they therefore
stop contracting)
9. diaphragm relaxes, & moves upward, resuming its
original shape
-rib cage relaxes & moves downward & inward & air is
forced out the lungs
• Thus, CO2 levels in blood regulate breathing rate.
Therefore, it is better to not give pure oxygen to a patient
to get breathing going (should be a mixture of oxygen and
carbon dioxide)
• Average human breathes in, on average, 500 ml of air per
breath (tidal volume)
• vital capacity: maximum that can be breathed in per
breath (averages about 3000-6000 ml.)
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• other part of this air is stuck in bronchioles and
doesn’t get to the alveoli. ( "Dead Air Space")
• residual air: air that remains in lungs after
expiration (about 1000 ml)
CONDITIONING OF INHALED AIR
On its journey into alveoli, the air is:
1. Cleansed of Debris:
- nose hairs & mucous in nasal passageways
- mucous lining & cilia of trachea and bronchi
2. Adjusted to Body Temperature.
- the more contact it has with moist tissues that are
37 C, closer the temperature of the inhaled air gets to
37 C.
- by time the air gets to alveoli, it has same
temperature as surrounding tissue
3. Adjusted to 100% Humidity:
- inhaled air becomes saturated with water
• only ~350 cc of the 500 cc normally breathed in actually
gets down deep enough to reach the alveoli
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SPECIALIZATION OF THE ALVEOLI
Alveoli are specialized for gas exchange with the blood:
1. very numerous: a great surface area for the diffusion
of gases
2. very thin walls: are only one-cell thick which aids in
gas diffusion because there is very little resistance
3. have a coating of lipoproteins on their inner
surface(SURFACTANT): helps to maintain surface
tension thus preventing them from collapsing and
sticking together during exhalation
4. supplied with stretch receptors: are nerve endings
that are sensitive to stretch
5. kept moist: ensures that gas exchange is possible. If
they dried out, efficient diffusion would be impossible
6. have a very rich blood supply from the pulmonary
capillaries to ensure maximum gas diffusion
EXTERNAL RESPIRATION:
• the exchange of gases between the air in the alveoli
and the blood in pulmonary capillaries
• exchange of gases is by diffusion alone (high
concentration to low concentration)
capillaries (blood)
Alveoli (lung)
[O2]
low
high
[CO2]
high
low
• Carbon dioxide is moved in the blood in three forms
a) HHb – reduced hemoglobin (H+ ions)
b) HbCO2 - carbaminohemoglobin
c) HCO3 – - bicarbonate ion
• As O2–poor blood enters the arteriole end of the
pulmonary capillary, conditions in the lungs that allow the
hemoglobin to drop H+ and CO2 and then pick up O2 are a
pH of 7.4 and a temperature of 37 C.
• CO2 that is dropped off by the hemoglobin (HbCO2)
simply diffuses out of the blood and into the alveoli
• The HHb drops off the H+ ions which then joins with
HCO3- to form H2CO3 (carbonic acid). In order to
maintain the pH of the blood this acid can not remain in
the blood. The enzyme carbonic anhydrase converts
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the carbonic acid into CO2 and H2O. These
molecules then diffuse out of the blood and into the
alveoli
• As CO2 is leaving the blood there is room for the
hemoglobin to carry oxygen as HbO2
(oxyhemoglobin). This O2 rich blood leaves the
capillaries and enters the pulmonary venules (and
veins) and heads back to the heart.
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• The CO2 and H2O enter the capillaries by diffusion. In
order to move the CO2 and H2O we must reassemble
them. The H2O and CO2 combine to form H2CO3
(carbonic acid) which is then converted into H+ ions
and HCO3-. The H+ is picked up by hemoglobin and
becomes HHb. The HCO3- stays in the blood and travels
in this form. A small percentage of CO2 joins with Hb
and travels as HbCO2. These three forms of CO2 leave
the capillary bed through the venule end and return to the
heart.
⇒
INTERNAL RESPIRATION:
• the exchange of O2 and CO2 between BLOOD in the
systemic capillaries and TISSUE FLUID.
• O2-rich blood enters the arteriole end of a systemic
capillary bed. The Hb releases the O2 allowing it to
diffuse into the tissues based on the conditions at the
cellular level.
• The conditions in the systemic capillaries that signal the
Hb to drop the O2 and pick up the H+ is a pH of 7.38 and
a temperature of 38 C.
• The O2 that diffuses in to the tissues is used for cellular
respiration. The products of cellular respiration are
ATP, CO2, and H2O. The latter two are waste products
and must be removed from the cell.
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Note: Hemoglobin combines with the excess H+ that this reaction
produces. That way, blood pH remains constant. You could
say that Hemoglobin acts like a buffer.
RESPIRATORY DISORDERS
1. Common Cold: Caused by viral infection. About 150
viruses are known to cause colds.
• Mild symptoms: sore throat, watery mucusy nasal
discharge.
• No Cure -- treat symptoms. Antihistamines,
decongestants, ASA, rest.
2. Influenza: a more severe viral infection.
• Symptoms include fevers, aches, cold symptoms.
Vaccines have been developed, but the virus is
constantly mutating into new forms. Over 20,000,000
people died in a flu epidemic in 1919-20.
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3. Bronchitis: usually caused by viral infection of nasal
cavities that spreads to bronchi and causes a secondary
bacterial infection.
• In acute bronchitis, there is heavy mucoid discharge,
coughing.
• Chronic bronchitis is not usually due to bacterial
infection, but rather to chronic irritation of bronchial
lining (leads to degeneration of lining, loss of cilia).
Chronic bronchitis is usually due to smoking.
• Treatment for acute bronchitis is antibiotics and rest.
4. Pneumonia: caused by bacteria or viruses which infect
lungs. The lobes of the lungs fill up with mucus and pus.
• Many AIDS patients die of Pneumocystis carinii
infection.
• Treatment is antibiotics (if bacterial), hospitalization.
5. Emphysema: most often caused by smoking.
• Deteriorating bronchioles ----> alveoli cut off. This leads
to ballooning of lungs due to trapped air. The trapped air
causes the alveoli to rupture.
• Symptoms include coughing, sluggishness, heart racing.
The heart and brain starve for oxygen. May lead to a
heart condition.
• Hard to treat: often surgical removal of some lung tissue
helps.
6. Tuberculosis: caused by tubercle bacteria. Can detect
with a skin test, X-Rays.
• If the bacilli invade lungs, cells the invaders with capsule
called tubercles (a defense mechanism). This may kill
sufferer.
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• Treatment: quarantine, antibiotics, other drugs.
7. Lung Cancer: Smoking is the #1 cause! (see text).
• Lung cancer is a progressive disease --> early detection
is important.
Progress of disease:
1. Lungs exposed to carcinogenic irritants.
2. Bronchial cells thicken, callus, cilia die.
3. "Atypical" cells start appearing in thickened lining ("in
situ" cancer).
4. Some of these cells break loose and penetrate other
tissues (= metastasis). This is the point where true
cancer begins.
5. Tumor(s) grow, tubes become blocked, lung collapses,
secondary infections can occur.
• Treatment: chemotherapy, surgery, pneumonectomy
(remove lung).
Smoking Risks (a partial list):
• lung cancer
• bronchitis/emphysema
• larynx cancer
• peptic ulcers
• bladder cancer • reduced lifespan
• pancreas
• weak immune system
cancer
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